Automatic air valves for duct systems, which both prevent the discharge of contaminated air therefrom and allow ambient air to enter the ducts when a negative pressure occurs therein (for example, upon the flushing of a water cabinet of a sanitation system), are well-known. Such air valves employ valve members which may be either "freely-movable" or "nonfreely-movable". The term "freely-movable" refers to those valve members which are intended to slide (in guides or otherwise) only in response to pressure and air flow. The term "nonfreely-movable" refers to those valves valve members which are constantly biased into, or are otherwise restrained in, a particular (normally closed) position.
Traditionally, such air valves employ nonfreely-movable valve members, such as the spring-loaded valve member disclosed in U.S. Pat. No. 2,405,241 issued to Smith. While valves employing such nonfreely-movable valve members operate effectively, they are not always as sensitive to changes in pressure as is desired or needed.
To increase the sensitivity of such automatic valves, it has been proposed to equip such automatic air valves with freely-movable valve members. Such automatic air valves that include freely-movable valve members are disclosed in U.S. Pat. Nos. 3,923,081 issued to Persson and 4,232,706 issued to Ericson.
In the variety of automatic valves that utilize freely-movable valve members to control the flow of air in and out of the duct, in order to attain the desired increase in sensitivity, the valve member must be capable of freely moving in response to even certain slight pressure and air movements. Accordingly, these freely-movable valve members are much more readily subject to being blocked, knocked out of alignment, or otherwise operatively interferred with. This can result in, for example, preventing the freely-movable valve member from being fully opened (unseated) or closed (seated). A major source of such blockage and interference are insects, small animals and other foreing objects, such as debris, which may enter the valve from the ambient enviroment and come into contact with the freely-movable valve member therein.
To solve the problem of blockage or interference resulting from such foreing object from the ambient enviroment, an automatic air valve was disclosed in U.S. Pat. No. 4,535,807 issued to Erisson. In this valve, a grill is disposed over the exterior end of the passageway through which the air passes into the conduit. This grill acts as a filter for preventing and protecting against the entry into the passageway of those foreign objects, thereby preventing them from coming into contact with, or otherwise interfering with, the proper operation of the freely-movable valve member.
While such an arrangement is extremely useful for preventing the entry of foreign objects from the ambient environment, it offers no protection whatsoever from foreign objects, such as insects, reptiles, small animals or other matter which originate from within the duct system itself. In warmer climates, such as in certain southern portions of the United States, it is common for insects and reptiles (such as snakes) to inhabit such duct systems, especially when the ducts are part of a sanitation system. These foreign objects that originate in the duct system can, despite the presence of the grills disclosed in Ericson '807, still comes in contact with, and/or otherwise interfere with, the proper operation of the freely-movable valve member (for example, by preventing the freely-movable valve member from being fully opened and/or closed), and of the automatic air valve.
Complicating this problem is the fact that sometimes these valves must be interposed directly in the conduit flow line of the duct system. In such cases, the valve must be equipped so that the flow of fluids and/or solids through the conduits of the duct system is not obstructed.
The use of interior filters in automatic air valves that employ nonfreely-movable valve members has also been disclosed. In Smith '241 an interior filter is utilized in a valve that employs as spring-loaded valve member. However, use of such a filter, as taught therein, is only for the purpose of preventing foreign objects in the ambient environment from entering the drain pipe via the valve and valve member. In this respect, foreign objects would come into contact with (and operatively interfere with) the valve member before they would be restrained by the filter.
Also, the filter disclosed by Smith '241 may be moved upwardly towards the valve member by, for example, a snake in the drain pipe, until the filter actually contacts the valve member. Such contact would operatively interfere with a freely-movable valve member. There is no means whatsoever suggested by Smith '241 to prevent such movement of the interior filter, so that it does not contact or otherwise operatively interefere with the valve member. There is no suggestion whatsoever to permit the use of interior filter described in Smith '241 to restrain foreign objects originating in the drain pipe from entering the valve and operatively interfering with the valve member. While such a feature may not be important in a valve employing a nonfreely-movable valve member, it is essential where use of a freely-movable is employed.
Finally, it is noted that the interior filters disclosed of which I am aware are planar plates that have a plurality of apertures or air passages formed therein. Unfortunately, such a shape effectively reduces the total air passage area of the valve, consequently reducing the sensitivity of the valve member. Once again, while such a feature is not essential in non-sensitive valves, such as the those that utilize nonfreely-movable valve members, it is essential for the proper operation of highly-sensitive valves that utilize freely-movable valve members.
Thus, it can be seen that there remains a need for an automatic air valve for ducts, and in particular for the ducts of a water system or a sanitation system, which employs a freely-movable valve member and which includes an interior filter by which foreign objects, such as insects, reptiles, small animals, etc., may be retained in the duct system, so that they are restrained from operatively interfering with the freely-movable valve member and, in combination therewith, a means which prevents the interior filter to move or be moved, so that the interior filter is prevented from operatively interfering with the freely-movable valve member. It can further be seen that there remains a need for such an automatic air valve, having such an interior filter which, in addition, does not restrict the flow of air therethrough.